Project Summary The long-term goal of this proposal is to develop a method for stable, heritable and cell-specific knock down of gene expression in the nematode C. elegans. The ability to knock down gene expression in individual cell types in this organism will allow a more detailed understanding of protein function in individual cells and will permit the dissection of cellular interactions such as those present in neural circuits. Our strategy usurps the nonsense-mediated decay (NMD) machinery present in all eukaryotic cells designed to degrade mRNA transcripts that contain premature termination codons. In our strategy we express the gene of interest with a 3'- untranslated region (UTR) that targets the mRNA transcript for degradation in wild-type cells but not in cells in which the NMD machinery has been compromised by mutation. Using cell-specific promoters we can then convert NMD deficient cells into NMD competent cells to cause cell-specific degradation of mRNA transcripts that contain NMD targeting 3'-UTRs. We will demonstrate the feasibility of this method by 1) knocking down the expression of a multicopy transgene encoding a fluorescent protein and 2) knocking down the expression of an endogenous signaling gene. We will quantify the amount of mRNA and protein in these knock down cells. This strategy can be used to knock down the expression of any gene in any cell in the organism. Because many of the proteins expressed in C. elegans have mammalian orthologs (~40% of all genes) our knock down strategy should lead to a better understanding of protein function in humans that will have far-reaching implications on human health. As one example, understanding how neurotransmitter receptors and their intracellular signaling partners function in specific cell types can lead to better therapies for disease states such as Parkinson's disease, schizophrenia and drug abuse.